How is it childish? Not all plumbers cost the same or do the same work. If you wanna hire a good plumber, you'll have to pay them more.

Likewise, if people on your team get better at their jobs and you don't want them to leave, you also have to pay them more.

Correct but not the point. The reason you pay your plumber 1x and not 2x is because someone else can do the same job equally well for you for 1x.

You don't pay 2x untill you are forced to (eg plumber is the only game on town) not because you are so enlightened.